Localization of the motor endplate zone in human skeletal muscles of the lower limb: anatomical guidelines for injection with botulinum toxin

Aim Botulinum toxin gives a local tone reduction by blocking neurotransmission at the motor endplate (MEP). The importance of using MEP-targeted injections is demonstrated in animal models and in a clinical human study. The goal of this review is to present the available data on the localization of the MEP zone of frequently injected muscles of the lower limb and to compare this with current practice. Method Current knowledge on the localization of the MEP zone is based on some older histological studies, and for some of the more frequently injected muscles also on more recent anatomical dissection. Results We find that for some muscles the MEP zone can be more precisely demarcated, and for many other muscles that its location is somewhat different than the currently injected areas in clinical practice. Optimal injection sites are presented for gastrocnemius, soleus, tibialis posterior, semitendinosus, semimembranosus, gracilis, biceps femoris, rectus femoris, adductor longus, brevis and magnus, and psoas muscles. Interpretation We propose optimal injection sites in relation to external anatomical landmarks for the frequently injected muscles of the human lower limb to facilitate the efficiency of botulinum toxin injections.